Brain electrode

ABSTRACT

The present invention relates to an electrode ( 1 ), in particular a deep brain stimulating (DBS) electrode or a deep brain lesioning electrode. The present invention also relates to a method for manufacturing the electrode ( 1 ) of the present invention and the use of the electrode. The present invention also relates to a directional electrode.

The present invention relates to an electrode, in particular a deepbrain stimulating (DBS) electrode or a deep brain lesioning electrode.The present invention also relates to a method for manufacturing theelectrode of the present invention and the use of the electrode.

Stimulating and lesioning electrodes are used in a variety of surgicalprocedures, in particular, DBS electrodes are used in a variety ofneurosurgical procedures.

A surgeon wishing to stimulate or lesion a particular area of nervoustissue, can target the end of an electrode to the target site so that adesired electrical current can be delivered. Numerous methods are knownfor targeting the electrode to the desired site including stereotacticmethods.

Generally, deep brain stimulating electrodes are manufactured by forminga coil of one or more insulated wires having non-insulated ends on asupport, welding electrode conducting areas on to the non-insulated endsof the wires and placing a sheath of non-conducting material over thenon-conducting parts of the electrode. It is clear that such a methodfor producing an electrode is laborious and therefore expensive.

Furthermore, as numerous parts are used in the construction of theelectrode, it is possible that the overall diameter of the electrodewill vary along its length. In particular, the electrode areas which arewelded on to the electrode, especially to spot weld points, can be proudof the rest of the surface of the electrode leading to difficulties ininserting the electrode. A further problem with electrodes constructedin this manner is that the electrode has to be of a sufficient size forit to enable electrode conducting areas to be welded onto thenon-insulated ends of the wires.

There is therefore a need in the art for an electrode which can beconstructed more efficiently and with greater accuracy.

It is becoming increasingly common for patients with disorders of brainfunction, including disorders of movement, intractable pain, epilepsyand some psychiatric disorders to be treated with deep brainstimulation. DBS electrodes are chronically implanted into the finetargets in the brain where electrical stimulation will disrupt abnormalneural firing in these patients to alleviate their symptoms. Braintargets for treating functional disorders are usually deeply situatedand of small volume. For example, the optimum target for treatingParkinson's disease is situated in the sub-thalamic nucleus (STN) and isa sphere of 3 to 4 mm in diameter or an ovoid of 3 to 4 mm in diameterand 4 to 5 mm in length. Other targets such as the globus pallidus (usedfor treating hyper- or hypo-kinetic disorders) or targets in thethalamus (used for treating tremor) are usually no more than 1 to 2 mmlarger.

Current DBS electrodes, for example those supplied by Medtronic Inc,Minneapolis, Minn., are of dimensions to accommodate such volumes. Forexample, such electrodes have a diameter of about 1.27 mm and have 4ring electrodes of the same diameter positioned at their distal end.Each ring electrode has a length of 1.5 mm with a 1.5 or 0.5 mmseparation. In use, the DBS electrode is connected to a battery drivenpulse generator via a cable and the equipment implanted subcutaneously,generally with the pulse generator positioned below the clavicle. Thefrequency, amplitude and pulse width of the stimulating currentdelivered to the electrode contacts can be programmed using externalinduction.

A problem with the use of such electrodes is the difficulty inaccurately placing the electrode within the desired target. The accuracyof placement is key to the effectiveness of the treatment. For a smalltarget such as the STN, misplacement of the electrode by no more than 1mm will not only result in sub-optimal symptomatic control but mayinduce unwanted side effects such as weakness, altered sensation,worsened speech or double vision (see FIG. 4).

The established method to place an electrode into a functional braintarget is first to localise the area of abnormal brain function. This isachieved by fixing a stereotactic reference frame to the patient's head,which can be seen on diagnostic images, and from which measurements canbe made. The stereotactic frame then acts as a platform from which theelectrode is guided to the target using a stereoguide that is set to themeasured co-ordinates.

However, functional neurosurgical targets are often difficult orimpossible to visualise on diagnostic images and so their actualposition may need to be inferred with reference to visible land marks inthe brain and using a standard atlas of the brain to assist the process.Due to anatomical variation between an individual and the atlas and evenbetween different sides of the same brain in an individual suchdifferences can lead to error in target localisation. Errors in targetlocalisation may also result from patient movement during imageacquisition or geometric distortion of images which can be intrinsic tothe imaging methods. Such errors may be further compounded at surgery byper-operative brain shift. This may result from the change in headposition from that during image acquisition to the position on theoperating table, from leakage of cerebrospinal fluid when a burr hole ismade with subsequent sinking of the brain and/or from the passage of theelectrode through the brain substance. Surgeons attempt to correct theseerrors by performing per-operative electrophysiological studies on thepatients undergoing functional neurosurgery who are kept awake duringthe procedures. These studies include microelectrode recording of theneural firing in the planned target area and/or stimulation of thetarget area using a test electrode. A series of passes are made throughthe target area with microelectrodes and sample recordings taken. Thetarget is defined by its characteristic patterns of firing. Because ofthe jelly-like consistency of the brain and the depth of the functionaltargets within it, there needs to be a space of about 2 mm betweendifferent microelectrode passes to prevent the electrode passing down apreviously made track. Thus, for a small target such as the STN, it ispossible for the recordings from two microelectrode passes, 2 mm apart,to both register location within the target structure but to findneither of them to be optimally located centrally within the target.Likewise, if a test stimulation electrode is passed just off the optimaltarget position, i.e. ±1 millimetre, then a second pass to correct thiserror will almost inevitably result in the electrode passing down thesame track.

If an electrode is placed exactly in the centre of a target having a 3mm diameter, then the distance from the electrode surface to the edge ofthe target is usually under 1 mm. If the current spreads beyond this,then side effects can be incurred. For these reasons, given the smallchance that an electrode will be placed in the centre of a target andthat a placement error of ±1 mm can result in sub-optimal treatment withside effects, which cannot readily be corrected with repositioning,there is a need for an electrode which overcomes at least some of theseproblems.

U.S. Pat. No. 5,843,148 discloses a high resolution brain stimulationlead, wherein the electrode comprises ring segments diagonally arrangedalong the circumference of the lead. Accordingly, in theory by passing astimulation current between electrode contact areas (i.e. ring segment),off axis stimulation can be achieved. Off axis stimulation refers to thegeneration of an electric field that is displaced to one side of theelectrode. Furthermore, by rotating the lead, different volumes oftissue around the lead circumference may be stimulated. The majorproblem with this device is that the diagonal geometry of the ringsegment results in a complex electric field which will spiral around theportion of the diameter of the electrode and is necessarily elongatedalong the axis of said electrode. The proposed configuration wouldtherefore not form an off axis electric field that is suitable fortreating a desired target. Furthermore, this device does not enable oneskilled in the art to adjust the volume of tissue being stimulated inboth the axial plane and the horizontal plane independently. Instead, onrotating the electrode, the volume of tissue stimulated varies in boththe horizontal and axial planes, making interpretation of patient'sresponses extremely difficult. Furthermore, the complex geometry of theproposed electrode would be difficult to construct and vulnerable tomechanical failure.

There is therefore a need for an electrode which overcomes at least someof the problems associated with the prior art electrodes.

In a first embodiment of the present invention there is provided anelectrode having a proximal and distal end comprising a core comprising:

-   -   (a) one or more insulated wires extending from the proximal end        to the distal end wherein the one or more insulated wires have        non-insulated ends, present at the proximal and distal ends;    -   (b) an insulating sheath around the core, wherein the        non-insulated ends of the one or more wires are not covered by        the insulating sheath; and    -   (c) one or more electrode conducting areas formed by depositing        electrically conducting material on the surface of the sheath,        wherein the one or more electrode conducting areas are in        electrical contact with at least one of the a non-insulated ends        of the one or more insulated wires.

The term “electrode” refers to any electrical conducting lead forenabling the production of an electric field at a desired site.Preferably the electrode is a DBS or deep brain lesioning electrode.Such electrodes are well known to those skilled in the art. The one ormore insulated wires are arranged so that an electric current can bepassed from the proximal end of the electrode to the distal end of theelectrode. Preferably a separate electrode conducting area is formed forthe end of each one or more insulated wires at the distal end of theelectrode. By making an electrical connection to the corresponding endof the wire at the proximal end, the electrode conducting area will beelectrically charged. Preferably electrode conducting areas are presentat one or both ends of the electrode.

The term “insulated” as used herein means electrically insulated. Theinsulated wires used in the electrode of the present invention can beany insulated wires. Preferably the insulated wires are made from gold,a gold alloy or a platinum/iridium alloy.

It is further preferred that the core of the electrode comprises aplurality of the insulated wires. It is particularly preferred that thecore comprises 3 or 4 insulated wires.

The insulating sheath can be made from any non-conductive material,preferably a plastics material. In particular, it is preferred that theinsulating sheath is made from polyurethane.

The purpose of the electrode of the present invention is to produce anelectric field at a desired target site. The electrode has a proximalend which, in use, is connected to an electricity source. The proximalend is preferably connected to the electricity source by the one or moreelectrode conducting areas present at the proximal end of the electrode.Preferably each electrode conducting area at the proximal end isconnected to an electrode conducting area at the distal end of theelectrode via an insulated wire. Electrode conducting areas at thedistal end are positioned, during use, at the target site and anelectric field is produced. Depending on the electrical connections madeat the proximal end, the electric field will be generated bycorresponding electrode conducting areas present at the distal end.Accordingly, it is possible to produce an electric field with differentelectrode conducting areas and furthermore it is possible to generateeither a mono-polar or bi-polar electric field. Altering the connectionsof an electrode to an electric source is well known to those skilled inthe art. In particular, the technical manual for Medtronic's DBS leads3389 and 3387 clearly discusses changing electrical connections at theproximal end of an electrode to change the electric field generated atthe distal end of the electrode.

The electrode of the first embodiment of the present invention ispreferably less than 2 mm in diameter, more preferably less than 1.5 mmin diameter, most preferably 1.27 mm in diameter. The electrode can beof any length and is preferably between about 10 cm and 30 cm in length.The length of the electrode will vary depending on the distance of thedesired target from an accessible surface of the patient.

The electrode conducting areas formed on the electrode can be anydesired shape. Preferably the electrode conducting areas are formed asannular rings around the electrodes. For producing a directionalelectric field areas such as squares or rectangles can be formed on apart of the circumference of the electrode. Preferably each electrodeconducting area extends over less than half, more preferably less than aquarter and most preferably between about an eighth and a sixteenth ofthe circumference of the electrode by restricting the size of electrodeconducting area. By restricting the area of the electrode conductingarea it is possible to produce a directional electrical field as isdiscussed in greater detail below.

Preferably the electrode conducting area is positioned on the electrodeso that its longitudinal axis is parallel to or perpendicular to thelongitudinal axis of the electrode. By ensuring that the electrodeconducting area is so orientated it is possible for the surgeon todetermine the effects of moving the electrode with greater ease.

Preferably the electrode conducting areas are rectangular in shape andthe longitudinal axis of the rectangle is parallel to the longitudinalaxis of the electrode. It is further preferred that the rectangles areabout 1.5 to 3 mm in length and about 0.2 to 0.5 mm in width. If thereis more than one electrode conducting area present on the electrode theelectrode conducting areas are preferably arranged in a line parallel tothe longitudinal axis of the electrode (See FIG. 5). Alternatively, itis preferred that each electrode conducting area is staggered along thelength of the electrode (see FIG. 6A). By ensuring that the electrodeconducting areas are staggered, it again allows greater flexibility tothe surgeon for producing the electric field at different positionsalong the length of the electrode on which the electrode conductingareas are positioned.

The electrically conducting material can be any material suitable forforming an electrode conducting area including metals, polymers etc.Preferably the electrically conducting material is gold or platinum.

The one or more electrode conducting areas can be formed by any method.Preferably, the electrode conducting areas are formed by depositingelectrically conducting material of the surface of the sheath. There arenumerous methods well known to those skilled in the art for depositingelectrically conducting material on the surface of various materials.Preferably the electrically conducting material is deposited by jetprinting, etching, photolithography, plasma deposition, evaporation,electroplating, or any other suitable technique.

Jet printing techniques are well known to those skilled in the art. Forexample, in U.S. Pat. No. 5,455,998, an ink jet head for depositingconductive ink onto a desired surface is disclosed. U.S. Pat. No.5,114,744 discloses a method for applying a conductive material to asubstrate using an ink jet. Furthermore, WO 99/43031 discloses a methodfor depositing by ink jet printing an electrode layer onto a device.

Etching methods for depositing electrically conducting material are alsowell known to those skilled in the art. In particular, such methods aredescribed in Plasma Etching in Microtechnology, Universiteit Twente,Fluitman and Elwenspoek, ISBN: 103650810x. See also Jansen et al,Journal of Micromechanics and Microengineering, 14-28, 1996.

Photolithography techniques are also well known to those skilled in theart and are described in Geiger et al, VLSI, Design Techniques forAnalogue and Digital Circuits, Chapter 2, 1990.

WO 90/33625 describes a process for depositing a conductive layer on asubstrate comprising depositing ink on the substrate by means oflithographic printing to form a seeding layer and then depositing anelectrically conducting layer.

There are numerous deposition techniques including evaporation,sputtering and vapour deposition. All these methods are described inVLSI Design Techniques for Analogue and Digital Circuits (supra).

Electroplating techniques are well known to those skilled in the art andhave been used for depositing electrically conductive material at adesired site on numerous materials.

A further method by which it is possible to deposit electricallyconducting material is by using conductive spray paint. Conductive spraypaint may be used in combination with an ink jet printing head.Furthermore, companies such as Precision Painting, Anaheim, Calif., havebeen applying electrically conductive coatings such as copper and nickelto a variety of objects. Accordingly, such methods can be used in orderto provide an electrically conducting material to a desired substrate.

By depositing electrically conducting material on the surface of thesheath, the electrode can be produced easily and inexpensively as it isno longer necessary to weld the electrically conducting parts to thenon-insulated ends of the wires.

The electrode of the first embodiment of the present invention is robustas it does not comprise welded contacts. Furthermore, by depositing theelectrically conducting material using the methods described above, itis possible to produce the electrode conducting areas precisely and invirtually any size and shape. Furthermore, the electrically conductingmaterial can be deposited as a thin coating ensuring that the diameterof the electrode does not increase significantly and therefore does notaffect the insertion of the electrode. The electrodes can also be madevery small (less than 1 mm in diameter) because it is not necessary tospot weld electrode conducting areas on to the electrode.

In a further preferred embodiment the electrode according to the firstembodiment of the present invention may have a flexible distal endallowing the distal end to be bent, using for example a J wire, so thatit can be moved to a desired position.

The present invention also relates to a method for constructing anelectrode according to the first embodiment of the present inventioncomprising:

-   -   coating a core comprising one or more insulated wires with an        electrically insulating sheath, wherein the non-insulated ends        of the one or more wires are not coated by the sheath;    -   and depositing electrically conducting material on the surface        of the sheath to form one or more electrode areas which are in        electrical contact with at least one of the non-insulating ends        of the one or more insulated wires.

Preferably, the core is formed by winding the one or more insulatedwires around a supporting member. Preferably the supporting member is atungsten wire. The supporting member is removed one the electrode isformed.

The electrically conducting material can be deposited by any method,including jet printing, etching photolithography, plasma deposition,evaporation and electroplating.

The present method is a simple and efficient method for the productionof electrodes and allows greater flexibility in the production of theelectrode conducting area on the electrode.

The method of the present invention can be automated to further reducethe cost of producing the electrode.

In the second embodiment of the present invention, there is provided adirectional electrode having a proximal end and a distal end comprising:

-   -   (a) a core comprising one or more insulated wires extending from        the proximal end to the distal wherein the one or more insulated        wires have non-insulated ends present at the proximal and distal        ends;    -   (b) an electrically insulating sheath around the core, wherein        the non-insulating ends of the one or more wires are not covered        by the insulating sheath; and    -   (c) one or more electrode areas in electrical contact with at        least one of the non-insulated ends of the wire, wherein each        electrode area extends over less than half the circumference of        the electrode.

The term “directional electrode” refers to an electrode which producesan electric field that it is not uniformly formed around thecircumference of the electrode. Instead the electric field is displacedto one side of the electrode. By having an electric field displaced toone side of the electrode, it is possible to change the position of theelectric field by rotating the electrode. This has the advantage thatwhen the electrode is placed in a sub-optimal position, it is possibleto rotate the electrode and thereby alter the position where theelectric field is produced relative to the target tissue, resulting inincreased flexibility of the system and enabling the production of anelectric field at an optimal position relative to the desired tissue.

By ensuring that the electrode conducting area extends over less thanhalf the circumference of the electrode, it ensures that the electricfield is displaced to one side of the electrode. Preferably, theelectrode conducting area extends over less than a quarter, morepreferably between about an eighth and a sixteenth of the circumferenceof the electrode. The smaller the electrode conducting area, the greaterdisplacement of the electric field generated. However, if the electrodeconducting area becomes too small (less than a sixteenth) it is possiblethat the electric field becomes toxic and causes tissue death usingconventional current supply levels. Accordingly, the amount ofdisplacement required can be altered by using different electrode areashaving different sizes. The directional electrode of the presentinvention may therefore comprise different sized electrode conductingareas which can be used in order to displace the electric field todifferent degrees.

It may be desirable to have a small electrode conducting area (e.g. lessthan a sixteenth of the circumference) when it is desired to causetissue death in a defined area.

As indicated above for the electrode of the first embodiment of thepresent invention, the electrode conducting area can be any shape. It isalso preferred that the longitudinal axis of the one or more electrodeconducting areas are parallel or perpendicular to the longitudinal axisof the electrode.

Preferably the one or more electrode areas are rectangular in shape andare about 1.5 to 3 mm in length and 0.2 to 0.5 mm in width.

The core, insulating wires and electrically insulating sheath of thedirectional electrode are as defined for the electrode according to thefirst embodiment of the present invention.

As for the first embodiment of the present invention, it is preferredthat the electrically conducting material, is gold or platinum.

It is further preferred that the directional electrode of the presentinvention comprises a mark at the proximal end of the electrode inalignment with the electrode areas for orientating the position of theelectrode areas. Preferably the mark is a line along the length of theelectrode. The line does not have to be continuous along the length ofthe electrode and is used by the surgeon in order to be able todetermine the position of the electrode conducting areas.

It is preferred that the directional electrode according to the secondembodiment of the present invention is a DBS electrode or a deep brainlesioning electrode.

As for the electrode of the first embodiment of the present invention,the directional electrode can be used to produce mono-polar current orbi-polar current.

The directional electrode of the second embodiment of the presentinvention can be constructed by any method, including the method used toconstruct the electrode according to the first embodiment of the presentinvention or via the prior art method comprising welding the electrodeconducting areas into place on the electrode.

The present invention further provides a method for constructing thedirectional electrode according to the second embodiment of the presentinvention comprising:

-   -   coating a core of one or more insulated wires having        non-insulated ends with an electrically insulating sheath,        wherein the non-insulated ends of the one or more wires are not        coated by the sheath; and    -   depositing electrically conducting material on the surface of        the sheath to form the one or more electrode areas which are in        electrical contact with a non-insulating end of the one or more        insulated wires.

Preferably electrically conducting material is deposited by jetprinting, etching, photolithography, plasma deposition, evaporation orelectroplating according to the method described in respect of theelectrode according to the first embodiment of the present invention.

The present invention also provides the use of the directional electrodeof the second embodiment of the present invention for use in therapy.Preferably the therapy is the surgical treatment of abnormalities ofbrain function, including abnormalities of movement such as Parkinson'sdisease, Chorea, tremor, multiple sclerosis and cerebral palsy;abnormalities of the mind including depression and obsessive compulsivestates, chronic pain syndromes and epilepsy. The directional electrodecan also be used to lesion brain tumours, especially in eloquent areas.

In use, the electrode is usually inserted over a supporting wire toprovide the required stiffness needed to insert the electrode into thebrain of a patient. Alternatively, and provided a plug is not insertedinto the end of the electrode, the electrode can be inserted over aguide wire and passed down the guide wire to the desired position.

Embodiments of the present invention will now be described by way ofexample only and with reference to the accompanying drawings, in which:

FIG. 1 shows a core of an electrode comprising four insulated wireswound on a tungsten wire support.

FIG. 2 shows a mould half for producing an insulating sheath around acore.

FIG. 3 shows (A) an electrode with protruding non-insulated wire ends,(B) an electrode having electrode conducting areas at one end, (C) anelectrode having electrode conducting areas at both ends, (D) a crosssection of the end of an electrode having a bung inserted in the end ofthe electrode.

FIG. 4 shows a schematic view of a desired target site and shows optimaland sub-optimal positions of an electrode.

FIG. 5 shows the distal end of a directional electrode comprising fourelectrode conducting areas arranged in a line.

FIG. 6 shows (A) the distal end of a directional electrode comprisingfour electrode conducting areas in a staggered arrangement, (B) shows asectional view of the electrode through line x-x.

EXAMPLES Example 1

Constructing an Electrode

An electrode (1) having a proximal end and a distal end is constructedby winding four platinum/iridium alloy insulated wires (diameter of 0.10mm) onto a tungsten wire (5) in order to form the structure shown inFIG. 1. Thus the ends of each platinum/iridium wire extend radially awayfrom the tungsten wire and are spaced apart along the length of thetungsten wire. This structure forms the core (3) of the electrode (1).The core (3) is then inserted into a mould (7) and a polyurethane sheath(9) cast around the core (3). The tungsten wire (5) is held undertension in the mould (7). The ends (4) of the insulated wires protrudefrom the sheath (9) formed around the core (3) and are then cut flush tothe surface of the sheath (9). By cutting the ends (4) of the wires sothat they are flush to the surface of the sheath (9), the metallic coreof the wires will be exposed on the surface of the sheath (see FIG. 3A).

Electrode conducting areas (11) are then formed on the sheath (9) and incontact with the metallic surface of each of the cut wires. Theelectrically conducting material used is platinum. The platinum isdeposited as a ring around the electrode (1) on the sheath (9) of theelectrode (1) to form an electrode conducting area (11) as a ring aroundthe electrode (1). FIGS. 3B and C clearly show the formation of theelectrode conducting areas (11) on the proximal and distal ends of theelectrode (1).

In this example the platinum is deposited by depositing ink on thesheath (9) by lithographic printing thereby forming a seeding layer, anddepositing platinum by electroless deposition (see WO 00/33262).

Once the electrode conducting areas (11) are formed on the sheath (9),the tungsten wire (5) is removed and a plug (15) is inserted in thedistal end of the electrode (1) (see FIG. 3D).

On inserting the electrode into the brain of a patient, a tungsten wireis inserted into the electrode to provide the electrode with sufficientrigidity for insertion.

In use, the proximal end of the electrode (1) is connected to a pulsegenerator. The electrode (1) can then be used to produce a mono-polarelectrical field or a bipolar electrical field (4) at the distal end ofthe electrode (1) depending on the electrical contacts made with thegenerator.

The resulting electrode (1) can be used in a variety of surgicalprocedures, in particular in a variety of neurosurgical procedures.

Example 2

Method of Constructing a DBS Directional Electrode

An electrode (1) is constructed in accordance with the method describedin Example 1 except that the platinum material deposited in order toform the electrode conducting areas (11) at the distal end of theelectrode is deposited in four discrete rectangles on one side of theelectrode (1) (see FIG. 5). Each electrode conducting area (11) isapproximately 1.5 mm long and 0.5 mm in width. The width constitutes 45°of the electrode's circumference as the electrode's diameter is 1.27 mm.A gap of 0.5 mm is formed between each electrode conducting area (11).The proximal end of the electrode (1) has electrode conducting areas(11) formed as rings in accordance with the method disclosed inExample 1. The electrode (1) also comprises a line (13) running alongthe length of the electrode (1) which is aligned with the electrodeconducting areas (11) and serves as an indicator of the orientation ofthe electrode conducting areas (11).

Example 3

Method of Constructing a DBS Directional Electrode with StaggeredElectrode Conducting Areas

In another example, the electrode conducting areas (11) are formed atthe distal end of the electrode (1) in a staggered arrangement (see FIG.6A). The electrode conducting areas (11) are about 3 mm in length and0.5 mm in width and each electrode conducting area (11) is separatedfrom its neighbour by 0.2 mm.

Use of the Directional Electrode

A directional DBS electrode (1) made according to Example 2 or Example 3is inserted into the brain of a patient so that the distal end of theelectrode (1) is placed at the desired target. The target is stimulatedto confirm accurate localisation and the electrode (1) is rotated inorder to ensure that the optimum position of the electrode conductingareas (11) is obtained. The indicated line (13) on the electrode (1)will assist with this orientation. The DBS electrode (1) is now fixed tothe patient's skull and connected to a generator that is implantedsubcutaneously in the patient. Generally, the electrode of Example 2will be used to produce a bipolar electric current and the electrode ofExample 3 will be used to produce a monopolar electric current.

If the electrode (1) position proves to be sub-optimal post operatively,then it is possible to try the alternative electrode conducting areas(11) in order to see if the position can be optimised by utilising oneof the alternative electrode conducting areas (11).

The directional electrode (1) enables the surgeon to be able to alterthe position of producing an electrical current by simply rotating theelectrode (1) by utilising other electrode conducting areas (11) formedon the distal end of the electrode (1).

1. An electrode comprising: (a) a core comprising one or more insulatedwires having non-insulated ends; (b) an insulating sheath around thecore, wherein the non-insulated ends of the one or more wires areexposed; and (c) one or more electrode areas formed by depositingelectrically conducting material on the surface of the sheath, whereinthe one or more electrode areas are in electrical contact with at leastone of the non-insulated ends.
 2. The electrode of claim 1 wherein thecore comprises a plurality of insulated wires having non-insulated ends.3. The electrode of claim 2, wherein each end of each insulated wire isin electrical contact with a separate electrode area.
 4. The electrodeof claim 1, wherein the electrically conducting material is deposited byjet printing, etching, photolithography, plasma deposition, evaporationand electroplating.
 5. The electrode of claim 1, wherein theelectrically conducting material is gold or platinum.
 6. The electrodeof claim 1, wherein the electrode is a deep brain stimulating (DBS) ordeep brain lesioning electrode.
 7. A method for constructing anelectrode according to claim 1 comprising: (a) coating the core of oneor more insulated wires with the electrically insulating sheath, whereinthe non-insulated ends of the one or more wires are not coated by thesheath; and (b) depositing electrically conducting material on thesurface of the sheath to form one or more electrode areas which are inelectrical contact with at least one of the non-insulating ends.
 8. Themethod of claim 7, wherein the one or more insultated wires are woundaround a supporting member.
 9. The method of claim 8, wherein thesupporting member is a tungsten wire.
 10. The method of claim 7, whereinthe electrically conducting material is deposited by jet printing,etching, photolithography, plasma deposition, evaporation andelectroplating.
 11. A directional electrode comprising: (a) a corecomprising one or more insulated wires having non-insulated ends; (b) anelectrically insulating sheath around the core, wherein thenon-insulating ends of the one or more wires are exposed; and (c) one ormore electrode areas on the surface of the sheath in electrical contactwith at least one of the non-insulated ends wherein each electrode areaextends over less than half the circumference of the electrode.
 12. Thedirectional electrode of claim 11, wherein each of the one or moreelectrode areas extends over less than a quarter of the circumference ofthe electrode.
 13. The directional electrode of claim 12, wherein eachof the one or more electrode areas extends over about an eighth of thecircumference of the electrode.
 14. The directional electrode claim 11,wherein the longitudinal axis of the one or more electrode areas areparallel to or perpendicular to the longitudinal axis of the electrode.15. The directional electrode of claim 11 wherein the core comprises aplurality of insulated wires having non-insulated ends.
 16. Thedirectional electrode of claim 15, wherein each end of each insulatedwire is in electrical contact with a separate electrode area.
 17. Thedirectional electrode of claim 16, wherein the plurality of electrodeareas are in a staggered arrangement.
 18. The directional electrode ofclaim 11, wherein the electrically conducting material is gold orplatinum.
 19. The directional electrode of claim 11, wherein theelectrode is a deep brain stimulating (DBS) or deep brain lesioningelectrode.
 20. The directional electrode of claim 11, comprising a linealong the length of the electrode in alignment with the electrode areasfor orientating the position of the electrode areas.
 21. The directionalelectrode of claim 11, which produces a monopolar current.
 22. Thedirectional electrode of claim 11, which produces a bipolar current. 23.A method for constructing the directional electrode of claim 11,comprising: (a) coating the core of one or more insulated wires with theelectrically insulating sheath, wherein the non-insulated ends of theone or more wires are not coated by the sheath; and (b) depositingelectrically conducting material on the surface of the sheath to formthe one or more electrode areas which are in electrical contact with atleast one of the non-insulating ends.
 24. The method of claim 23,wherein the one or more insulated wires are wound around a supportingmember.
 25. The method of claim 24, wherein the supporting member is atungsten wire.
 26. The method of claim 23, wherein the electricallyconducting material is deposited by jet printing, etching,photolithography, plasma deposition, evaporation and electroplating. 27.Use of the directional electrode of claim 11 in therapy.
 28. A brainelectrode arranged to produce an effective field which is offset to oneside of the electrode and which has a plane of symmetry through a planethrough the longitudinal axis of the electrode.
 29. A method of making abrain electrode comprising the steps of: arranging an elongateconductive electrode core in a mould cavity, arranging a conductor tocontact the core and to extend outside the cavity of the mould, castingmoulding material into the cavity of the mould to form a coating on thecore so that the conductor creates a path to the core through thecoating.